Ventilation, Castelli style. You won't find a more mesh-based approach to indoor bike shorts than these Insiders. The lightest and coolest bottom in the Castelli line, it features mesh side panels for super ventilation and the high compression performance required for long stationary rides. For unmatched comfort, it's outfitted with the Progetto X2 Air Donna chamois, a yoga-style waistband, and raw-cut, gripper-free leg bands to provide a secure fit that won't ride up. Pair with the Insider Top to become the star pupil of your next spin class.